Interleukin-1 (IL-1) plays an important role in the pathogenesis of several inflammatory disorders. Two forms of IL-1 proteins have been described, interleukin-1-alpha (IL-1.alpha.) and interleukin-1-beta (IL-1.beta.). This application will use the terms IL-1.alpha. and IL-1.beta. to denote the respective forms of IL-1 proteins consistent with the usage of such terms in the scientific literature. See: Young et al. "Human Interleukin Ib is not secreted from Hamster Fibroblasts when expressed constitutively from transferred cDNA", Journal of Cell Biology, Vol. 107, 447-455 (1988). Both forms of IL-1 are synthesized as approximately 31 kDa precursor molecules that are subsequently processed to generate 17 kDa mature molecules. Although both forms of IL-1 are secreted proteins, each protein lacks signal peptides. The mechanism of the secretion has not been fully defined.
IL-1.alpha. and IL-1.beta. are products of distinct genes. The proteins share only 27-33% of their amino acids even though each protein has a similar biological activity and interact with the same receptor. IL-1.alpha. precursor (preIL-1.alpha.) is almost as active as the mature form. In contrast, IL-1.beta. precursor (preIL-1.beta.) has no biological activity until further processed to a mature form. This application will use the term mature, bioactive IL-1.beta. (matIL-1.beta.) to highlight and emphasize that a precursor composition has been processed to the mature, active composition. In humans, IL-1.beta. is the predominant species and may play a more important role in certain disease states.
Only certain cell types process preIL-1.beta. and secrete matIL-1.beta.. Monocytes and macrophages are the most efficient producers and secretors of IL-1.beta.. Of the two forms of IL-1 synthesized and secreted following activation of monocytes and macrophages, IL-1.beta. is the most abundant form.
The cellular processing of preIL-1.beta. to mature, bioactive IL-1.beta. is mediated by the enzyme ICE, a cysteine protease. ICE is synthesized as a 45 kDa precursor molecule which is processed in vivo to form fragments of 20 and 10 kDa. These two fragments are combined or folded, in vivo, to form the active enzyme.
IL-1.beta. plays a critical role in the pathogenesis of several inflammatory, autoimmune, and leukemic disease states. Thus, an understanding of the release and processing of IL-1.beta. and its precursors is desired. The present knowledge is, in part, limited by a lack of models on the cellular level for the making and processing of IL-1.beta.. In vivo, at the cellular level, monocytes and macrophages produce small quantities of IL-1.beta., for only a limited time. It is difficult to grow monocytes and macrophages for long periods of time. There are large differences and variations between freshly prepared monocytes and macrophages. In naturally occuring cells, it is difficult to study preIL-1.beta. and ICE interactions. As a consequence, the role of various regions or domains of preIL-1.beta. and ICE in the processing, activation and release of ICE and IL-1.beta., and the structural significance of various amino acid residues remain unclear.
A consistent model capable of alteration and manipulation is desired to further the understanding of the release and processing of IL-1.beta. and ICE and as a screen for compositions which may interact with the processing and release of IL-1.beta. and ICE. A consistent model that mimics the induction of preIL-1.beta. upon the application of a stimulus, and consistently expresses ICE, is desired.
Compositions which alter the production, processing and release of IL-1.beta. and ICE have interest as therapeutics to modulate the inflammation response. IL-1.beta. and ICE themselves may also have utility to modulate inflammatory responses.